Hydrogen-producing fuel-processing systems include a hydrogen-producing region that is adapted to convert one or more feedstocks into a product stream containing hydrogen gas as a majority component. This may be accomplished through a variety of mechanisms, such as steam reforming, autothermal reforming, partial oxidation, and pyrolysis. In all of these examples, a fuel, which may be a carbon-containing feedstock such as a hydrocarbon or an alcohol, is combined with an oxygen-containing substance, which may be an oxygen source such as air, oxygen-enriched air, bottled oxygen, water, and/or steam to produce hydrogen gas.
In particular, hydrogen-generating regions that produce hydrogen gas with a steam reforming reaction combine a carbon-containing feedstock (such as methanol or natural gas) and water (in the form of steam) to produce hydrogen gas as a majority component, together with carbon monoxide and carbon dioxide as minority components. Other minority components also may be present in both the feed and product streams. In steam reforming reactors, it is important to control the steam-to-carbon (S/C) ratio of reactants entering the reactor, as a high S/C ratio may cause water to condense in downstream processes, limit system efficiency, and/or impact the overall water balance of the hydrogen-producing fuel processing system. In contrast, low S/C ratios may result in deactivation of the reforming catalyst due to the formation of carbon within the reactor and/or corrosion of the reactor vessel due to metal dusting.
Tight control of the S/C ratio may be accomplished through the use of high-quality feed streams of known composition and purity, together with accurate pumps and/or mass flow control devices that enable precise metering of both the steam stream and the carbon-containing feedstock stream as they enter the steam reformer. In practice, such purity and precision may be difficult and/or costly to achieve and the cost may not always be justifiable. Thus, there exists a need for efficient and cost-effective alternatives that consistently maintain the desired S/C ratio.